1. Field of the Invention
The present invention relates to a vehicle frame structure for motorcycles which is suitable for increasing the maneuvering capability of the vehicle, improving the productivity at the time the vehicle body is assembled, reducing the size of the vehicle, and simplifying the vehicle frame structure.
2. Description of Background Art
Known vehicle frame structures for motorcycles are disclosed in, for example, {circle around (1)} Japanese patent No. 2945094 entitled “Electric two-wheeled vehicle” and {circle around (2)} Japanese patent No. 2963337 entitled “Motorcycle”.
FIG. 5 of the above publication {circle around (1)} shows a motorcycle having left and right main frames 13 extending rearwardly from a head tube 12. A swing arm 24 is swingably mounted on rear portions of the main frames 13 by a pivot shaft 23. A rear wheel 29 is mounted on a rear end of the swing arm 24. Furthermore, a cushion unit 30 (see FIG. 1) is interposed between the swing arm 24 and the main frames 13.
FIG. 6 of the above publication {circle around (1)} shows a vehicle frame 11 having a battery case 70 mounted between the main frames 13 and a battery 68 housed in the battery case 70.
FIG. 1 of the above publication {circle around (2)} shows a motorcycle having a main frame 4 extending rearwardly from a head pipe 2. An engine 6 is mounted on the main frame 4. A swing arm 5 is swingably mounted on a rear portion of the main frame 4 by a pivot shaft 49. A rear wheel 7 is mounted on a rear portion of the swing arm 5. Furthermore, a shock unit 11 has a lower end attached to a lower portion of the swing arm 5 by a link 13 and an upper end attached to a crankcase 12 of the engine 6.
FIG. 2 of the above publication {circle around (2)} shows the main frame 4 in plan.
Generally, vehicle frames have left and right main frames extending rearwardly from a head tube. Since the main frames are widely spaced apart from each other, electric parts or other parts can be disposed in the space between the main frames. According to the arrangement shown in the above publication {circle around (1)}, the space between the rear upper portions of the main frames 13 is small because the end of the cushion unit 30 is attached to the rear upper portions of the main frames 13.
Inasmuch as parts to be disposed in the space between the rear upper portions of the main frames 13 need to be disposed separately in other locations, their weights are distributed, posing disadvantages on racing or off-road vehicles which require high maneuvering capabilities.
With the parts being disposed separately, the worker needs to install the parts on the vehicle while moving around. This results in a reduction in productivity and an increase in the size of the vehicle.
According to the arrangement shown in the above publication {circle around (1)}, the battery case 70 is mounted between the main frames 13. Accordingly, the manpower required to manufacture the motor vehicle is increased and the cost to manufacture the motor vehicle is also increased.
According to the arrangement shown in the above publication {circle around (2)}, the upper end of the shock unit 11 is attached to the crankcase 12 of the engine 6 which is positioned higher than the rear end of the main frame 4. Accordingly, the space between the rear portions of the main frame 4 cannot be utilized as effectively as the arrangement shown in the above publication {circle around (1)}.